The first application of anaerobic biological processes to the treatment of organic wastes was the septic tank, invented in 1895. A variety of applications of the anaerobic concept have evolved over the past nearly 100 years. Early applications, beginning in 1918, were to the treatment of sludges from domestic sewage. Much later, beginning in the 1950's, a process that was variously called "anaerobic contact" and "anaerobic activated sludge" was applied to livestock slaughtering wastewaters. This process made use of a separate solids separation or clarifier unit. Still later, beginning in the 1970's, anaerobic treatment applications included various attached growth (upflow, downflow, and expanded bed) treatment approaches.
The anaerobic contact process developed in the 1950's makes use of a reactor tank in which contact between the anaerobic microorganisms and the wastewater occurs. The wastewater then flows through a vacuum degasifier to remove dissolved gases to enhance solids settling and then on to a separate solids searation unit in which biomass solids settle to the bottom for recycling to the contact tank. In these systems, multiple vessels are required resulting in high capital investment and inefficiencies due to the need to transfer the materials to a separate vessel for individual process steps.
Those concerned with these and other problems recognize the need for an improved anaerobic sequencing batch process.